Horse Health

The ‘Hind Gut Acidity’ Problem

It’s the trendy diagnosis, but is it a dangerous ride?


Hind gut acidity, sometimes used synonymously with hind gut ulcers, is blamed for a staggering array of signs ranging from poor appetite, cracked hooves, right hind lameness and any undesirable behavior trait you can mention. It’s bad enough that there is virtually no scientific justification for most of this. Worse yet is that the treatments suggested could be harmful.

Enteroliths are stones that form inside the intestines when minerals precipitate around a core of nondigestible material. The core could be things like a wood fragment, piece of string or bit of rubber fencing. Most enteroliths are composed of struvite—magnesium ammonium phosphate.

Enteroliths are stones that form inside the intestinal tract.
Enteroliths are stones that form inside the intestinal tract.

Several factors have been identified as risks for enterolith formation. High intake of magnesium, phosphorus or protein is certainly one. The ammonium forms from bacterial breakdown of protein. Risk factors can vary between cases but one universal finding is an alkaline environment in the large intestine. If you are feeding your horse a product to increase pH/reduce acidity in the large intestine you are increasing the risk of enterolith formation, especially if the horse didn’t need it in the first place. A mildly acidic pH in the high 6’s is normal for the cecum.

What if the horse doesn’t have an acidity problem and the supplement makes their hind gut more alkaline than normal? Is more better? No. The intestinal milieu is a very complex network with many different species of organisms interacting synergistically in an environment where their food sources and pH requirements are compatible. If you artificially change the environment, some species will die and fermentation will suffer.

Some people are advised to feed their horse the drug ranitidine (Zantac) to control hind gut acidity, allegedly because it works better than omeprazole for the hind gut. Both of these drugs reduce stomach acid. Since there are no acid secreting cells in the hind gut, there is no reason to think either one would help. It is normal for the stomach to be extremely acidic. The horse’s body takes care of this by secreting very large amounts of bicarbonate into the small intestine.

The system is so effective pH goes from an acidic low of 2 in the stomach to the mid to high 6’s in the small intestine. The body makes all the bicarbonate it needs from an endless supply of water and carbon dioxide. To look at any proposed role of stomach acid in hind gut ulcers another way, why wouldn’t you see ulcers showing up in large numbers and greater severity in the small intestine which is exposed to stomach contents before they even reach the hind gut? There is no mention of small intestinal ulcers in the postmortem dissections.

Is there a problem with reducing the load of stomach acid just in case? Yes, there is. Stomach acid is there for a reason. It is the first line of defense against intestinal infections. It activates an enzyme that starts protein digestion in the stomach. Stomach acid is also needed to break supplemental minerals into their ionic form so they can be absorbed.

Treating a condition that does not exist can be harmful. If you are concerned about hind gut acidity, ask your vet to test fecal pH first (between 6.2 and 6.5 is the usual range).


All content is for informational purposes only. Contact your local veterinarian if you have any questions regarding the health of your animals.

 About the Author

Eleanor Kellon is the Staff Veterinary Specialist for Uckele Health and Nutrition. Dr. Kellon also offers private nutritional consultations and online courses through Equine Nutritional Solutions. Find out more at

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